Mechanical anisotropy of aligned fiber reinforced composite for extrusion-based 3D printing

3D printing techniques are being researched extensively in the construction sector. However, the key issue lies in the development of cementitious materials with both favorable printability and enough mechanical capability by means of high strength and ductility. In this study, an optimal basalt fiber content was determined basing firstly on suitable printability and then on mechanical performance. A self-developed 3D printer was used for extrusion of the cementitious material and also for mechanical enhancement of fiber alignment along the print direction by keeping the nozzle diameter smaller than the length of the basalt fiber. The printing process deposits directional filaments, intrinsically resulting in laminated structures and mechanical anisotropy. Anisotropic performances of the printed material were evaluated by direction-based mechanical performance testing and confirmed by ultrasonic pulse velocity testing. The mechanical behaviors of 3D printed samples exposed to compressive, tensile, flexural and shearing loadings were experimentally investigated. The mesoscale structures of printed samples were detected through the advanced CT scanning technique. Both mechanical and acoustic indexes were proposed to evaluate the anisotropic properties of printed materials. In particular, empirical relationships between the mechanical anisotropic properties and ultrasonic signals were established. On the microstructural level, mechanical enhancement of fiber alignment, fiber pullout and fiber fracture were all probed through scanning electron microscope (SEM) imaging.